Figure 1. Extremely dense electron–positron pair production from near-critical-density plasmas.

Two counter-propagating ultraintense laser pulses are focused from two directions onto the near-critical-density plasmas filled inside two cones (purple). The quivering electrons in the ultraintense laser fields experience large radiation-reaction forces by emitting photons so that a large number of electrons are trapped in the laser fields. These trapped electrons perform extreme oscillations in the transverse direction and emit bright γ rays (red- and blue–yellow) around the laser axis. Finally, copious numbers of e⁻e⁺ pairs are created via the multi-photon Breit–Wheeler process.